This invention generally relates to the treatment of the raw materials used in glass making. In particular, the invention is directed to an improved method of preparing discrete bodies of raw materials to be fed to glassmaking furnaces.
In this application the terms "glass" or "insoluble glass" will be applied to the familiar insoluble materials, while the term "soluble glass" or "soluble silicate glass" will be applied to those materials that consist of alkali metal and silica and are dissolved to form the commercial class of materials known as silicates.
Soluble and insoluble silicate glasses are formed by the fusion of glass-forming materials in a furnace or hearth which is commonly called a glass tank. The raw materials are charged to the furnace heated to a temperature above the initial fusion point of the glass batch raw materials to form a molten bath. Such raw materials are generally referred to as "batch" and the "batch" ingredients common to most glasses are sodium carbonate (soda ash) and a source of silica such as sand. Other widely used ingredients primarily used in the production of insoluble glasses include: lime, limestone, borax, potash, alumina and salt cake. The "batch" is charged to the furnace and floats on the molten glass bath until it melts and reacts to become part of the bath which is eventually drawn from the furnace as the product.
The usual glassmaking practices are energy-intensive and, indeed, inefficient. The "batch" floating on the molten glass is almost a perfect insulator, which prevents rapid heat transfer to the molten glass. The glass must have a considerable residence time in the furnace to achieve homogeneity. This increased holding time also requires more energy. In addition, loose "batch" cannot be preheated efficiently.
In recent years, some attempts have been made to improve this process and the manner in which heat is utilized. In general these attempts involve agglomerating the "batch" in some manner and then pre-heating these materials before charging them to the furnace. U.S. Pat. Nos. 3,542,534; 3,607,190; 3,726,697; 3,788,832; 3,800,639; 3,953,190; 4,023,976; 4,045,197 and 4,135,904 among others disclose various means for attempting to increase the efficiency of the glassmaking process. These techniques can achieve some increased heat utilization since furnace combustion gases are used as a source of heat. U.S. Pat. No. 4,023,976 cited hereinbefore is believed to be representative of the art that is most relevant to my improved process.
The prior art methods of preparing discrete bodies, usually briquettes, involve mixing a liquid binder, (water, caustic, silicate solutions, etc.) with the batch materials to form a moist, clinging mass of particles which is then compressed in some sort of die, roller or extruder to form the desired discrete bodies. There are several problems associated with such prior art methods. The addition of a substantial amount of moisture to the materials that constitute glassmaking batches can cause a significant portion of said batch to stick to batch handling equipment such as mixers and conveying equipment. Complete consolidation of the batch is also possible when using such methods. In addition, moisture added as part of, or as the total, binder must be removed prior to glass formation, at an undesirable expenditure of energy. It is apparent that there can be some significant improvements in the preparation of discrete, compacted bodies to be charged to glassmaking furnaces. It is an object of this invention to minimize the problems encountered in forming the desired discrete bodies such as briquettes.